Desire to be thin linked to genetics

Despite being bombarded with messages promoting being thin, not all women respond in the same way. AAP

Eating disorders that stem from a desire to be thin can be blamed in part on genetics, according to a new US study.

The study, published this week in the International Journal of Eating Disorders, found genetics may make some women more vulnerable to the pressure of being thin.

“We’re all bombarded daily with messages extolling the virtues of being thin, yet intriguingly only some women develop what we term thin ideal internalisation,” said Jessica Suisman, lead author on the study and a researcher at Michigan State University.

The study, which included 300 female twins aged 12-22, measured how much they wanted to look like people from movies, TV and magazines. Identical twins were compared with fraternal twins to establish the role of genetics in thin idealisation.

The heritability of thin idealisation was found to be 43%, meaning almost half of the reason women differ in their idealisation of thinness can be explained by their genetic make-up.

“We’ve known for a long time that there’s a substantial genetic contribution to just about any personality style,” said Tracey Wade, professor of psychology at Flinders University.

“This study helps establish people’s susceptibility to getting caught up in the thin ideal that is presented in the media.”

However John Hopper, director of the Australian Twin Registry, cautioned that the finding of a greater similarity between identical twins than between non-identical in the study could also be due to non-genetic causes.

“Identical twins share environmental and lifestyle factors more than do non-identical twins, especially during the age range of 12-22 years of twins in the current study. Therefore the estimate of "heritability” is likely an over-estimate,“ Professor Hoper said.

Dr Wade said there were a range of environmental and genetic contributors that could lead to eating disorders.

"To get a truly environmental variable is rare because our genes play a role in selecting our environments.” For example, she said impulsive people were more likely to suffer adverse life events.

Girls aged between 13 and 15 were most vulnerable to being exposed to environmental and genetic risks that could lead to them developing an eating disorder, Professor Wade said.

“That’s the age when you really want to try and help them not focus on weight and shape, to help them negotiate adverse events, and help them focus on identity rather that what they look like.”